1. Field of the Invention
This invention broadly relates to methods and apparatus for making orthodontic appliances such as brackets and buccal tubes. More particularly, the present invention concerns orthodontic appliances having a bonding surface for attachment to a tooth, and the bonding surface is shaped as desired in accordance with the selected treatment objectives. The present invention also concerns indirect bonding transfer apparatus that includes one or more appliances having a contoured bonding surface.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to desired locations in the oral cavity. Orthodontic treatment can improve the patient's facial appearance, especially in instances where the teeth are noticeably crooked or where the jaws are out of alignment with each other. Orthodontic treatment can also enhance the function of the teeth by providing better occlusion while eating.
One common type of orthodontic treatment involves the use of tiny, slotted appliances known as brackets. The brackets are fixed to the patient's teeth and an archwire is placed in the slot of each bracket. The archwire forms a track to guide movement of teeth to desired locations.
The ends of orthodontic archwires are often connected to small appliances known as buccal tubes that are, in turn, secured to the patient's molar teeth. In many instances, a set of brackets, buccal tubes and an archwire is provided for each of the patient's upper and lower dental arches. The brackets, buccal tubes and archwires are commonly referred to collectively as “braces”.
In the past, metallic orthodontic appliances including brackets and buccal tubes were often welded to bands. Each band was adapted to encircle one of the patient's teeth and provide a secure connection between the tooth and the appliance. Typically, a composition such as a band cement was applied to the inner surface of the band before placement on the tooth in order to fill any gaps or voids between the band and the tooth enamel and help prevent the band from “rocking” on the tooth.
However, metallic bands are generally considered unaesthetic and contribute to an undesirable “metallic mouth” appearance. Moreover, for a proper fit, each band must be carefully selected so that its size and shape match the size and shape of the patient's tooth. Additionally, bands are not considered suitable for use with appliances made of non-metallic materials, such as ceramic and plastic.
In recent years, there has been great interest in the use of appliances that are bonded to the enamel surface of the teeth by an adhesive. These appliances are not mounted on metallic bands and consequently the patient's appearance is improved. In addition, the expense of the bands, as well as the time needed to select the bands and attach the appliances to the bands, can be avoided.
However, it is important that any appliance that is adhesively bonded to a tooth remain firmly attached to the tooth over the entire course of treatment. Orthodontic appliances are sometimes subject to significant forces in the oral cavity due to the presence of a food object that may be located between the appliances and the teeth during mastication. These forces can be relatively large when the patient is chewing a relatively hard food object such hard candy or ice, and may in some instances cause the appliance to debond from the tooth.
Unfortunately, the progress of the orthodontic treatment program can come to an abrupt halt when an orthodontic appliance unintentionally debonds from a tooth. In that event, the patient should immediately return to the practitioner for re-attachment or replacement of the appliance so that treatment can resume. The time and expense of both the practitioner and the patient that is incurred to respond to a spontaneously debonded appliance is considered a nuisance that is best avoided.
As a result, manufacturers of orthodontic appliances often go to great lengths to ensure that their appliances remain firmly adhered to the teeth over the entire course of treatment. To this end, the base of the appliances is often provided with features to improve the strength of the bond between the appliance and the tooth. As one example, the base may have a concave, compound contour that closely matches the convex, compound surface of the tooth so that a mating fit is obtained. As another example, the base may include mechanical or chemical features such as projections, recesses or chemical treatments that serve to enhance the strength of the bond between the adhesive and the appliance. However, appliances are typically manufactured and sold with bases having a shape that matches the expected shape of a statistical “average” patient, which may or may not be similar in shape to the tooth of the particular patient undergoing treatment.
In addition, in many types of orthodontic techniques, the shape of the appliance base is an important factor for helping to ensure that the teeth move to their intended final positions. For example, one common type of orthodontic treatment technique is known as the “straight-wire” technique, where the resilient archwire tends to follow a smooth curve that lies in a horizontal plane at the conclusion of treatment. If, for instance, the convex shape of the patient's tooth is oriented in a direction that is different than the orientation of the concave shape of an appliance made for an “average” patient, the appliance will not be properly oriented to the tooth and the archwire slot will extend at an improper angle relative to the tooth for straight-wire treatment. As the archwire assumes a level, straight configuration near the end of the treatment program, the improperly oriented appliance will cause the tooth to assume a corresponding, improper position.
Other aspects of the shape of the appliance base are also important. For example, it may be desirable to provide a base having a “wedge-shaped” configuration, so that the long axis of the tooth is pivoted or tipped toward a certain pre-selected orientation as the archwire assumes the configuration of a smooth, horizontal curve near the end of the treatment program. In this regard, it is possible to orient the shape of the wedge so that the tooth is pivoted in a rotational direction about its long axis, or alternatively so that the long axis of the tooth is tipped along either a mesial-distal reference axis or a labial-lingual reference axis.
In general, orthodontic appliances that are adapted to be adhesively bonded to the patient's teeth are placed on the teeth by either one of two methods: a direct bonding method, or an indirect bonding method. In the direct bonding method, the appliance and adhesive are grasped with a pair of tweezers or other hand instrument and placed by the practitioner on the surface of the tooth in an approximate desired location. Next, the appliance is shifted along the surface of the tooth as needed until the practitioner is satisfied with its position. Once the appliance is in its precise, intended location, the appliance is pressed firmly onto the tooth to seat the appliance in the adhesive. Excess adhesive in areas adjacent the base of the appliance is removed, and the adhesive is then allowed to cure and fix the appliance firmly in place. Typical adhesives include light-curable adhesives that begin to harden upon exposure to actinic radiation, and two-component chemical-cure adhesives that begin to harden when the components are mixed together.
While the direct bonding technique described above is in widespread use and is considered satisfactory by many, there are shortcomings that are inherent with such a technique. For example, access to surfaces of malposed teeth may be difficult. In some instances, and particularly in connection with posterior teeth, the practitioner may have difficulty seeing the precise position of the bracket relative to the tooth surface. Additionally, the appliance may be unintentionally bumped from its intended location during the time that the excess adhesive is being removed adjacent the base of the appliance.
Another problem associated with the direct bonding technique described above concerns the significant length of time needed to carry out the procedure of bonding each appliance to each individual tooth. Typically, the practitioner will attempt to ensure that each appliance is positioned in its precise, intended location before the adhesive is cured, and some time may be necessary before the practitioner is satisfied with the location of each appliance. At the same time, however, the patient may experience discomfort and have difficulty in remaining relatively motionless, especially if the patient is an adolescent. As can be appreciated, there are aspects of the direct bonding technique that can be considered a nuisance for both the practitioner and for the patient.
Indirect bonding techniques often avoid many of the problems noted above. In general, indirect bonding techniques known in the past have involved the use of a transfer tray having a shape that matches the configuration of at least part of a patient's dental arch. A set of appliances such as brackets are releasably connected to the tray at certain, predetermined locations. Adhesive is applied to the base of each appliance, and the tray is then placed over the patient's teeth until such time as the adhesive hardens. Next, the tray is detached from the teeth as well as from the appliances, with the result that all of the appliances previously connected to the tray are now bonded to the respective teeth at their intended, predetermined locations.
In more detail, one method of indirect bonding of orthodontic appliances includes the steps of taking an impression of each of the patient's dental arches and then making a replica plaster or “stone” model from each impression. Optionally, a soap solution (such as Model Glow brand solution from Whip Mix Corporation) or wax is applied to the stone model. A separation solution (such as COE-SEP brand tinfoil substitute from GC America, Inc.) is then applied to the stone model and allowed to dry. If desired, the teeth of the model can be marked with a pencil to assist in placing the brackets in ideal positions.
Next, the brackets are bonded to the stone models. Optionally, the bonding adhesive can be a chemical curing adhesive (such as Concise brand adhesive from 3M) or a light-curable adhesive (such as Transbond XT brand adhesive or Transbond LR brand adhesive, from 3M). Optionally, the brackets may be adhesive precoated brackets such as those described in U.S. Pat. Nos. 5,015,180, 5,172,809, 5,354,199 and 5,429,229.
A transfer tray is then made by placing a matrix material over the model as well as over the brackets placed on the model. For example, a plastic sheet matrix material may be held by a frame and exposed to radiant heat. Once the plastic sheet material has softened, it is placed over the model and the brackets. Air in the space between the sheet material and the model is then evacuated, and the plastic sheet material assumes a configuration that precisely matches the shape of the replica teeth of the stone model and the attached brackets.
The plastic material is then allowed to cool and harden to form a tray. The tray and the brackets (which are embedded in an interior wall of the tray) are then detached from the stone model and sides of the tray are trimmed as may be desired. Typically, the adhesive that previously attached the brackets to the stone models remains connected to the brackets. This adhesive has an outer surface that subsequently provides a bonding surface for attaching the brackets to the patient's teeth in the oral cavity. In some instances, this bonding surface will have a contoured shape that roughly matches the shape of the replica tooth structure as well as the patient's tooth structure.
Once the patient has returned to the office, a quantity of adhesive is placed on the base of bracket, and the tray with the embedded brackets is then placed over the matching portions of the patient's dental arch. Since the configuration of the interior of the tray closely matches the respective portions of the patient's dental arch, each bracket is ultimately positioned on the patient's teeth at precisely the same location that corresponds to the previous location of the same bracket on the stone model.
Both light-curable adhesives and chemical curing adhesives have been used in the past in indirect bonding techniques to secure the brackets to the patient's teeth. If a light-curable adhesive is used, the tray is preferably transparent or translucent. If a two-component chemical curing adhesive is used, the components can be mixed together immediately before application of the adhesive to the brackets. Alternatively, one component may be placed on each bracket base and the other component may be placed on the tooth surface. In either case, placing of the tray with the embedded brackets on corresponding portions of the patient's dental arch enables the brackets to be bonded to the teeth as a group using only a short amount of time that the patient is occupying the chair in the operatory. With such a technique, individual placement and positioning of each bracket in seriatim fashion on the teeth is avoided.
A variety of transfer trays and materials for transfer trays have been proposed in the past. For example, some practitioners use a soft sheet material (such as Bioplast tray material from Scheu-Dental GmbH) for placement over the stone model and the appliances on the model. A vacuum is applied to draw the soft material into intimate contact with the model and the appliances on the model. Next, a stiffer sheet material (such as Biocryl sheet material, from Scheu-Dental GmbH or Great Lakes Orthodontics, Ltd.) is formed over the softer sheet material, again using a vacuum forming technique. The stiffer material provides a backbone to the tray, while the softer material initially holds the appliances and yet is sufficiently flexible to release from the appliances after the appliances have been fixed to the patient's teeth.
It has also been proposed in the past to use a silicone impression material or a bite registration material (such as Memosil 2, from Heraeus-Kulzer GmbH & Co. KG). The silicone material is applied over the appliances that are attached to the study model so that the appliances are partially encapsulated.
In an article entitled “A New Look at Indirect Bonding” by Moskowitz et al. (Journal of Clinical Orthodontics, Volume XXX, Number 5, May 1996, pages 277 et sec.), a technique for making indirect bonding trays is described using Reprosil impression material (from Dentsply International). The impression material is placed with a syringe over brackets that have been previously placed on a stone model. Next, a sheet of clear thermoplastic material is drawn down over the impression material using a vacuum-forming technique. The resultant transfer tray is then removed from the model for subsequent placement on the patient's dental arch.
Indirect bonding techniques offer a number of advantages over direct bonding techniques. For one thing, and as indicated above, it is possible to bond a plurality of brackets to a patient's dental arch simultaneously, thereby avoiding the need to bond each appliance in individual fashion. In addition, the indirect bonding tray helps to locate all of the brackets in their proper, intended positions such that adjustment of each bracket on the surface of the tooth before bonding is avoided. The increased placement accuracy of the appliances that is often afforded by indirect bonding techniques helps ensure that the patient's teeth are moved to their proper, intended positions at the conclusion of treatment.
While the indirect bonding techniques as described above have proven satisfactory for many practitioners, there is a continuing need to improve the state of the art. Moreover, there is a need to improve methods and apparatus for providing an appliance with a bonding surface that is especially adapted for the particular patient at hand.